<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 100px;
            height: 50px;
            border: 2px solid red;
            /*值越大越圆 超过宽高一半为正圆*/
            border-radius: 10px;
        }
    </style>
</head>
<body>
<div>这是div</div>
</body>
</html>